1. Field of the Invention
KOH is the last name of the inventor, and this invention is called KOH flue gas recirculation power plant with waste heat and byproduct recovery.
The invention relates to a process for power generation, which is both environmentally sound and cost-effective. More specifically, the invention relates to a process of burning any combustible material for efficient power generation, elimination of air pollutants and carbon dioxide emissions, and recovery of liquid nitrogen dioxide, liquid sulfur dioxide, and liquid carbon dioxide.
2. Description of the Prior Art
A conventional power plant consisting of a combustion furnace, a steam boiler, steam turbines, and a dust collector has been implemented for power generation and steam production for several, decades. Conventional power plants, particularly for coal-fired plants, emit a huge amount of nitrogen oxides, sulfur dioxide, carbon monoxide, particulate matters, heavy metals, and incomplete combustion products. Since air pollution control requirements become more stringent from time to time, power plants must be equipped with more sophisticated and expensive pollution control systems to meet regulatory emission limits. For sulfur oxides emission control, a flue gas desulfurization system or a fluidized bed combustion furnace is widely used. For nitrogen oxides emission control, power plants have implemented a combustion flue gas recirculation for staged combustion with steam or water injection, low NOx burners, selective catalytic reduction systems, non-selective catalytic systems, or any combination thereof to meet the emission limits.
Since the 1980""s, the integrated gasification combined cycle (IGCC) concept has been explored extensively. IGCC uses an oxygen stream for coal gasification and produces a gaseous stream consisting of methane, hydrogen sulfide, carbon monoxide, ammonia, etc. The gaseous stream passes through a sulfur removal system such as a Claus plant before burning in a gas turbine. In addition to requiring an expensive sulfur removal system, an IGCC plant must implement a nitrogen oxides removal system in order to meet regulatory requirements.
Since the Kyoto Accord for reduction of carbon dioxide, which is a greenhouse gas that causes global warming and associated climatic changes, coal-fired power plants have been extensively scrutinized. Although a coal-fired power plant is still the most cost-effective in power generation, its carbon dioxide emission is more than two times that of a natural gas fired plant. An MEA scrubbing system using monoethanolamine as absorbing agent has been implemented to recover carbon dioxide from combustion flue gases, but it is still not cost-effective. To enhance carbon dioxide recovery, oxygen is increasingly proposed as a replacement of air in fuel burning to reduce the volume of combustion flue gases and to increase the concentration of carbon dioxide in combustion flue gases.
U.S. Pat. No. 5,906,806 issued to Clark proposes to burn fuel using oxygen, water, and a recirculated combustion stream from a baghouse in two combustion furnaces. For additional air pollution control, Clark""s proposal requires several expensive control systems, which include an electron beam reactor, an ozone oxidation chamber, and an electrostatic precipitator with catalytic reactor. In addition, the combustion product discharged to the atmosphere still contains some incomplete combustion products and nitrogen oxides and excess oxygen discharged with combustion flue gases reduces utilization of oxygen generated by an air separation unit.
U.S. Pat. 6,196,000 issued to Fassbender proposes to burn fuel using oxygen and liquid carbon dioxide recovered from combustion process. For enhancing thermodynamic efficiency and carbon dioxide recovery, Fassbender proposes to operate an elevated pressure power plant. All operating units including a reaction chamber, a combustion chamber, a catalyst chamber, a hydrocone, heat exchanges, and condensers are under extremely high pressure, ranging from 300 to 5000 psia. A pressurized vessel requires additional power to operate and become a safety concern. In addition, the pressurized power plant still vents to the atmosphere a combustion flue gas stream containing some air pollutants and oxygen.
The invention is an integrated combustion process for efficient power generation, recovery of waste heat and byproduct, and elimination of air pollution. A combustion furnace, air separation units, a steam boiler with an economizer, a dust and acid gas removal system, several condensers, and absorption refrigeration units are integrated with two combustion flue gas recirculation loops to enhance steam production and to prevent combustion flue gases from being discharged into the atmosphere.
When oxygen is used instead of air for fuel combustion, the temperature of combustion products is extremely high. For combustion temperature control, the first combustion flue gas recirculation loop is implemented to recirculate part of the combustion gas stream from the economizer to the combustion furnace. How much of the combustion flue gas stream from the economizer to be recirculated back to the combustion furnace greatly depends on the chemical composition and heat content of fuel.
The combustion flue gas stream from the economizer, which is not recirculated back to the combustion furnace, passes through an oxygen-enriched stream heater for additional waste heat recovery, a fly ash and acid gas removal system, and several byproduct condensation units. After leaving the carbon dioxide condenser, it mixes with an oxygen-enriched stream from the air separation unit and flows back to the combustion furnace. The purpose of the second combustion flue gas recirculation loop is to eliminate any incomplete combustion products in the combustion furnace and reuse oxygen present in the combustion flue gas stream. Therefore, a combustion process designed according to the invention does not discharge combustion flue gases and air pollutants to the atmosphere. The nitrogen-enriched stream from the air separation unit is used in the condensers for byproduct recovery.
Absorption refrigeration units are integrated with the process to recover and convert waste steam from steam turbines to cooling. Cooling generated by absorption refrigeration units is used for enhancing condensing processes as well as providing extra cooling for industrial, commercial, or residential uses.